Many people suffer from either myopia (short-sightedness) or hyperopia (long-sightedness). The prevalence of myopia is increasing, leading to increased attention to the development of solutions to deal with myopia. In addition, for many people, myopia progresses over time, despite correction using some existing methods.
FIG. 1 shows an eye that is normal sighted (i.e. is neither long-sighted nor short-sighted, also called “emmetropic”). FIG. 2 shows a myopic eye viewing a distant object; the focal point of the image is located in front of the retina. This shifted focal point relative to the retina creates blur. Different myopic eyes may have different magnitudes of myopic blur. For example the retina of another eye may be located at the broken lines shown in FIG. 2, this other eye experiencing less myopic blur. Conversely to myopia, a hyperopic eye has a focal point located behind the retina, which also creates blur.
Several techniques have been used to correct myopia and hyperopia. These techniques include prescribing spectacle lenses or contact lenses, surgical implantation of an intraocular lens (e.g. an anterior chamber phakic intraocular lens), surgical reshaping/remodelling of the cornea and temporary reshaping/remodelling of the cornea by hard or soft contact lenses. Corneal remodelling using soft contact lenses is described in International Patent Publication WO 2005/022242 A1, the content of which is incorporated herein in its entirety.
International patent publication WO 2005/055891 A1, the content of which is also incorporated herein in its entirety, describes the use of a contact lens to control the relative curvature of field with an objective of controlling the progression of myopia or hyperopia. The method includes moving image points at the peripheral retina forwards or backwards respectively relative to the retina, while allowing for clear central vision. Corneal remodelling to achieve desired peripheral refraction is described in international patent publication WO 2008/014544 A1, the content of which is also incorporated herein in its entirety.
When looking at near objects, it has been observed that many individuals with myopia accommodate less than the amount that is needed to bring the image forward onto the retina. This under-accommodation is often referred to as lag of accommodation (or “accommodative lag”). FIG. 3 shows a myopic eye with lag of accommodation; the focal point of the image is located behind the retina. In a study involving children of primarily European descent, lag of accommodation measured at 33 centimetres using an autorefractor found the median lag to be 1.26D (range from −0.75 to 2.82D) in children aged 8 to 11 yrs. In children of Chinese ethnicity, lag of accommodation measured at 33 centimetres was 0.74+/−0.27D. Attempts have been made to treat accommodative lag. For example, United States patent publication number US 20040237971 A1 describes the control of the optical aberrations to reposition medium and high spatial frequency peaks to alter accommodative lag.
Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.